Beagle 2 was an unsuccessful British landing spacecraft that formed part of the European Space Agency's 2003 Mars Express mission. All contact with it was lost upon its separation from the Mars Express six days before its scheduled entry into the atmosphere. The Beagle 2 was named after HMS Beagle, which twice carried Charles Darwin during expeditions which would later lead to the theory of evolution.

Beagle 2 was conceived by a group of British academics headed by Professor Colin Pillinger of the Open University, in collaboration with the University of Leicester. Its purpose was to search for signs of life on Mars, past or present, and its name reflected this goal, as Professor Pillinger explained:

A point at 10.6°N, 270°W in Isidis Planitia, a large flat sedimentary basin that overlies the boundary between the ancient highlands and the northern plains of Mars, was chosen as the landing site. The lander was expected to operate for about 180 days and an extended mission of up to one Martian year (687 Earth days) was thought possible. The Beagle 2 lander objectives were to characterize the landing site geology, mineralogy, geochemistry and oxidation state, the physical properties of the atmosphere and surface layers, collect data on Martian meteorology and climatology, and search for possible signatures of life.

The Beagle is a breed of small to medium-sized dog. A member of the Hound Group, it is similar in appearance to the Foxhound, but smaller, with shorter legs and longer, softer ears. Beagles are scent hounds, developed primarily for tracking hare, rabbit, and other game. They have a great sense of smell and tracking instinct that sees them employed as detection dogs for prohibited agricultural imports and foodstuffs in quarantine around the world. Beagles are intelligent, and are popular as pets because of their size, even temper, and lack of inherited health problems. These characteristics also make them the dog of choice for animal testing.

Although beagle-type dogs have existed for over 2,000 years, the modern breed was developed in Great Britain around the 1830s from several breeds, including the Talbot Hound, the North Country Beagle, the Southern Hound, and possibly the Harrier.

Beagles have been depicted in popular culture since Elizabethan times in literature and paintings, and more recently in film, television and comic books. Snoopy of the comic strip Peanuts has been promoted as "the world's most famous beagle".